1. Field of the Invention
The present invention relates to a substrate processing apparatus for processing any of various kinds of substrates such as semiconductor wafers, glass substrates for liquid crystal displays, and substrates for PDPs (plasma display panels).
2. Description of Related Art
A semiconductor device fabrication process typically includes the step of repeatedly subjecting a semiconductor wafer (hereinafter referred to simply as "wafer") to film formation and etching processes to form fine patterns on a surface of the wafer. Since the surface of the wafer and the surface of a thin film formed thereon should be kept clean for fine processing thereof, the wafer is subjected to a cleaning process as required. For example, after a wafer or a thin film formed on the surface thereof is polished with the use of a slurry or abrasive, the slurry remains on the wafer surface; therefore, it is necessary to clean the wafer for removal of the slurry.
The wafer cleaning process for the removal of a slurry remaining on a wafer surface conventionally employs a disk brushing device, the construction of which is schematically illustrated in FIG. 5. A cleaning brush 1 is disposed above a wafer W held on a spin chuck (not shown). The cleaning brush 1 is attached to a distal end of a pivot arm 3 with its face downward, the pivot arm 3 being pivotal about a pivot shaft 4. The cleaning brush 1 can be rotated and revolved by pivoting the pivot arm 3. Further, the pivot shaft 4 is movable vertically, so that the cleaning brush 1 can be moved up and down between a processing position where the brush 1 abuts against the wafer W and a stand-by position where the brush 1 is retracted to the upper side of the wafer W.
To perform the cleaning process, the spin chuck is rotated at a high speed, thereby rotating the wafer W about a vertical center axis thereof. The cleaning brush 1, while being rotated about its axis, is scanned on the surface of the wafer W radially outwardly from the center thereof. Thus, the entire surface of the wafer W is subjected to a scrubbing process, and contaminants removed through the scrubbing process are forced out of the wafer W. The cleaning of the wafer W is achieved in this manner.
To ensure a constant cleaning effect, the cleaning brush 1 should be pressed against the surface of the wafer W with a proper pressure. Conventionally, the pivot shaft 4 is vertically moved by means of a pulse motor, and the directing pulse number for the drive of the pulse motor is adjusted by an operator so that the depression of the cleaning brush 1 with respect to the wafer W can properly be adjusted through visual observation.
However, the adjustment based on the visual observation by an operator inevitably entails errors, because the judgment criteria vary due to differences in the physical sensitivity among individual operators on different occasions. Further, precise adjustment cannot be ensured on the basis of the visual observation. It is therefore impossible to constantly provide for the maximum cleaning effect. In addition, the adjustment is performed less frequently because the operation of the apparatus should be temporarily stopped for the adjustment. It is therefore difficult to properly perform the adjustment operation in accordance with the wear or deformation of the cleaning brush. Further, the adjustment through the visual observation is troublesome.